1. Field of the Invention
The present invention relates to an ophthalmologic operation microscope, and more particularly to an ophthalmologic operation microscope equipped with a front lens for observing the eyeground of the eye to be examined.
2. Description of the Related Art
Usually, an ophthalmologic operation is conducted with microscopic observation. JP2002-350735A (paragraph [0016]–[0018], FIG. 6, FIG. 7, and FIG. 9) discloses an example of a microscope for such ophthalmologic operation. In the ophthalmologic operation microscope as disclosed in the above publication, a front lens is arranged between the objective lens and the eye to be examined, making it possible to illuminate the interior of the eye. This enables the operator to perform operation, in particular, eyeground operation, with surgical instruments in both hands. As shown in FIGS. 6 and 9 of the above-mentioned publication, the front lens is detachably arranged between the objective lens and the eye.
Further, as shown in FIG. 7 of the above-mentioned publication, in the ophthalmologic operation microscope as disclosed therein, illumination light is applied to the eye through an illumination prism provided so as to be offset from the optical axis of the observation optical system.
When, however, illumination light is applied from a direction oblique to the optical axis of the observation optical system, there are observed two reflection images of the exit pupil of the illumination optical system due to the reflective action of the refraction surfaces of the front lens. That is, the front lens has two refraction surfaces, and, when seen from the direction of the optical axis of the observation optical system, the reflecting positions of the two refraction surfaces reflecting the exit pupil differ from each other, with the result that two reflection images are observed.
Such reflection images lead to deficiency in visual field for the operator and constitute light spots in the observation image, making it rather difficult to observe the portions around the same.